This invention relates to liquid sterilizers and more particularly to water sterilizers employing ultra-violet radiation to kill bacteria.
It is well known to sterilize water by exposing the water to ultra-violet radiation at a wavelength of approximately 2537 Angstroms. In a typical sterilizer, water is exposed to ultra-violet radiation as it is introduced through an inlet into a cylinder housing an ultra-violet tube, the water then flowing through the length of the cylinder where it exits through an outlet. The water is sterilized as it is exposed to the ultra-violet radiation generated by the tube.
It is also known to sterilize water by exposing the water to ozone generated at a wavelength of approximately 1880 Angstroms. The ozone can be generated by means of a tube of similar construction to that of an ultra-violet radiation generator, or by means of an electrical arc generated in the water. The known ozone generator leaves a residue of ozone in the water, which continues to sterilize the water as it passes through the cylinder.
It is also possible to sterilize water utilizing gamma ray radiation. Thus, the principles of this invention apply to all of these known kinds of sterilizers. However, the invention will be specifically described with reference to embodiments employing ultra-violet radiation.
Although sterilization of water by use of ultra-violet radiation has an excellent reputation for killing bacteria, such sterilizers have tended to be expensive, and also require specialized skills for installation and maintenance. However, there is a need for a water sterilizer that a home or cottage owner can afford and can install and maintain without having specialized skills.
One of the problems associated with known sterilizers, which contributes to their complexity, is that they are designed as permanent installations, except for the replacement of worn out or defective bulbs. As a consequence, these sterilizers have complex mounting arrangements for the tube, the end seal connections and the water inlet and outlet. Also, because the known sterilizers were designed as permanent installations, the water supply connections tended to be complex, again requiring specialized skills for installation. Since the tubes are also quite delicate, there is a serious risk of tubes being broken on replacement, if done by anyone other than a trained technician.
An example of a prior art sterilizer of complex design is described in Canadian Pat. No. 610,989, which issued to Corn Products Company on Dec. 20, 1960. This patented sterilizer was clearly designed as a permanent installation except for replacement of the ultra-violet tubes. For example, the inlet and outlet ports are formed of conduits, nipples, adapters, gaskets and screws. The ends of the ultra-violet tubes are connected to electrical sockets that are mounted on connector blocks slidably mounted on connector block plates and locked in place. When a tube is to be replaced, these connectors have to be removed from the connector blockplates. It can be readily appreciated that specialized skills are thus required both for initial installation and maintenance. Resealing of the sterilizer when replacing a lamp also poses a problem.
As is well known, ultra-violet tubes operate more efficiently at higher temperatures. One known type of water sterilizer, therefore, provides a protective quartz sheath surrounding the tube, thereby leaving an air space between the sheath and the tube to provide insulation for the tube from the water flowing around the sheath. However, such sheaths suffer from the disadvantage of having to be cleaned periodically to remove collected dust, which can inhibit the penetration of light from the tube through the sheath to the water, resulting in reduced efficiency and risk of non-sterilization. Thus, the cleaning of the sheaths has to be done by a skilled technician. Special handling is also required, especially because the quartz is susceptible to finger prints, and because the quality of quartz required produces a fragile sheath that can be broken very easily. From the above discussion, it can be appreciated that prior art water sterilizers employing sheaths are expensive and require specialized skills for their installation and maintenance. Canadian Pat. No. 610,989 employes such a quartz sheath, adding to the complexity, fragility and cost of the sterilizer.
Other known prior art sterilizers employ sensing devices to sense the amount of light radiated by the ultra-violet tube, coupled with an electro-magnetic control device to control valves at the water inlet. Thus, if the tube is not emitting sufficient light to sterilize, the valve at the inlet is closed and the unit fails safe. Although serving a useful purpose, such fail safe devices add to the expense of a sterilizer unit. A prior art sterilizer employing such a fail safe device is described in Canadian Pat. No. 674,555, which issued to Allsafe Water Sterilizer Ltd. on Nov. 19, 1963. The Allsafe sterilizer is another example of one employing a protective sheath and designed as a permanent installation except for replacement of lamps, again involving a complex mechanical end cap arrangement requiring specialized skills for maintenance.
Canadian Pat. No. 767,856 granted Sept. 26, 1967 and Canadian Pat. No. 841,135, granted May 5, 1970, and invented by James W. Harrison, are further examples of sterilizers that are designed to fail safe. The sterilizers described in these patents are of the permanent installation type requiring the removal of end caps for replacement of ultra-violet tubes.